docs: def find_one(self, spec_or_id, **kwargs):
          """Get a single document from the database.
          
          All arguments to :meth:`find` are also valid arguments for
          :meth:`find_one`, although any `limit` argument will be
          ignored. Returns a single document, or ``None`` if no matching
          document is found.
          """
          if spec_or_id is not None and not isinstance(spec_or_id, dict):
              spec_or_id = {"_id": spec_or_id}
          kwargs['limit'] = -1
          self.find(spec_or_id, **kwargs)